The unit with the best price-to-performance ratio.

20 Phoenixes do indeed win against 10 Bears, but only if they attack first. And there will be 8 left, not 11.

With zero attack/defense stats, at least 11-12 Phoenixes remain, and this number depends slightly on who attacks first. However, in real games, the hero with the Bears usually has some attack stats, and the higher they are, the stronger the Bears become...